As an optical subscriber system construction technology to realize FTTH (Fiber to the Home), PON that has couplers placed in an optical fiber becomes generally popular due to a reduced fiber laying cost, which is one of its merits.
FIG. 1 is a configuration diagram of an example of a PON system. In FIG. 1, an OLT (Optical Line Terminal) 11 outputs an optical multiplexed signal in which optical signals of user data #1-#3 are modulated with time-division multiplexing. The optical multiplexed signal is split by an optical splitter 12 in three ways, each of which is transmitted to one of ONUs (Optical Network Units) 16, 17, and 18 with different-length optical fibers 13, 14, and 15, respectively.
The ONU 16 demodulates the original data #1 from the optical multiplexed signal. The ONU 17 demodulates the original data #2 from the optical multiplexed signal. The ONU 18 demodulates the original data #3 from the optical multiplexed signal.
Incidentally, a technology to multiplex subcarriers for OFDM signals with TDM (Time Division Multiplexing) is proposed (for example, refer to Patent Document 1).
Also, a technology for executing multi-rate transmission is proposed by changing the number of subcarriers for multi-carrier signals (for example, refer to Patent Document 2).